Historic Prussian blue (PB) pigment is easily obtained as an insoluble precipitate in quantitative yield from an aqueous mixture of Fe 3+ and [Fe II (CN) 6 ] 4− (Fe 2+ and [Fe III (CN) 6 ] 3−). It has been found that the PB pigment is inherently an agglomerate of 10-20 nm nanoparticles, based on powder x-ray diffraction (XRD) line broadenings and transmission electron microscopy (TEM) images. The PB pigment has been revived as both organic-solvent-soluble and water-soluble nanoparticle inks. Through crystal surface modification with aliphatic amines, the nanoparticles are stably dispersed from the insoluble agglomerate into usual organic solvents to afford a transparent blue solution. Identical modification with [Fe(CN) 6 ] 4− yields water-soluble PB nanoparticles. A similar ink preparation is applicable to Ni-PBA and Co-PBA (nickel and cobalt hexacyanoferrates). The PB (blue), Ni-PBA (yellow), and Co-PBA (red) nanoparticles function as three primary colour inks.

We have revealed the fundamental mechanism of specific Cs(+) adsorption into Prussian blue (PB) in order to develop high-performance PB-based Cs(+) adsorbents in the wake of the Fukushima nuclear accident. We compared two types of PB nanoparticles with formulae of Fe(III)4[Fe(II)(CN)6]3·xH2O (x = 10-15) (PB-1) and (NH4)0.70Fe(III)1.10[Fe(II)(CN)6]·1.7H2O (PB-2) with respect to the Cs(+) adsorption ability. The synthesised PB-1, by a common stoichiometric aqueous reaction between 4Fe(3+) and 3[Fe(II)(CN)6](4-), showed much more efficient Cs(+) adsorption ability than did the commercially available PB-2. A high value of the number of waters of crystallization, x, of PB-1 was caused by a lot of defect sites (vacant sites) of [Fe(II)(CN)6](4-) moieties that were filled with coordination and crystallization water molecules. Hydrated Cs(+) ions were preferably adsorbed via the hydrophilic defect sites and accompanied by proton-elimination from the coordination water. The low number of hydrophilic sites of PB-2 was responsible for its insufficient Cs(+) adsorption ability.

Electrocatalytic water splitting to oxygen and hydrogen has much attention as one of the most promising approaches for sustainable production of hydrogen as a carbon-neutral fuel. To establish efficient electrocatalytic...

An insoluble solid of historic Prussian blue (PB) was transformed into dispersible PB nanoparticles in water and various hydrophilic and hydrophobic organic solvents. Via hybrid surface modification using Na 4 [Fe II (CN) 6 ] and short-chain alkylamines, the insoluble PB was successfully dispersed in hydrophilicand-hydrophobic boundary alcohols, such as n-butanol. The n-butanol-dispersible PB nanoparticles afforded homogeneous spin-coated thin films on various substrates. The chemisorbed shorter-chain alkylamines, n-propylamines, of the PB nanoparticles were thermally released at 100 °C from their surfaces to present stubborn electrochromic PB thin films adhering to the substrate via mutual coordination-bonding networks.

Cs+ adsorption selectivity caused by hydration energy and percolation theory to evaluate the ion-exchangeable site ratio.

The critical bottleneck for water splitting, which is important for sustainable production of hydrogen, has remained in sluggish oxygen evolving reaction (OER) requiring insufficiently low overpotentials, η. We report a facile and versatile method for the preparation of loading-controllable metal oxide films adhered rigidly on electrode substrates, enabling effectual material hunting for superior OER anodes. This allows us to discover a ternary FeNiWO x film on a nickel foam (NF), attaining the lowest overpotentials of η 10 = 167 (the superscripts represent the attained current densities of 10 mA cm −2 ) with a Tafel slope of 49 mV dec −1 and at least 100 h stability in OER, which compare advantageously with only a few state-of-the-art OER anodes with excellent η 10 < 200 mV. The electrochemical data indicate synergistic coupling among ternary metal centers of Ni, Fe, and W to decrease the η value. The OER current is pH dependent for the FeNiWO x film, showing a non-proton-concerted process in the rate-determining step for OER. This could be explained by coupling of two neighboring lattice O •− radicals to form an O−O bond. The 3d bands of Fe or Ni could be stabilized by the high positive charge on W 6+ to become close to or penetrate the 2p band of lattice O 2− . This not only decreases the highest oxidation energy level for OER but also allows fast electron transfer from the 2p band of O 2− to the 3d band in the Fe IV or Ni IV state to form the O •− radicals.

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10 S cm . Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 10 -fold enhancement of proton conductivity, reaching ca. 10 S cm . The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.

Our experimental and theoretical studies elucidate the redox-coupled ion transport mechanism and the intrinsic structure–property relationship in binder-free Prussian-blue electrodes.